SAA-C03 Design Secure Architectures Practice Question
Exhibit
CloudTrail event summary:
- eventSource: kms.amazonaws.com
- eventName: Decrypt
- errorCode: AccessDeniedException
- userIdentity: arn:aws:sts::444455556666:assumed-role/PartnerUploadRole/partner-app
- requestParameters.keyId: arn:aws:kms:us-east-1:111122223333:key/6b2f-9a7c
Current CMK key policy excerpt in account 111122223333:
{
"Sid": "EnableRootPermissionsOnly",
"Effect": "Allow",
"Principal": { "AWS": "arn:aws:iam::111122223333:root" },
"Action": "kms:*",
"Resource": "*"
}Based on the exhibit, a partner account uploads encrypted objects to a central S3 bucket and later reads them back. The S3 permissions are correct, but the requests still fail. What change is required so the partner workload can use the customer-managed KMS key safely?
⚠ Common exam trap
Watch out — candidates often assume S3 bucket policies alone control all access, forgetting that SSE-KMS introduces a separate authorization layer at KMS that requires explicit cross-account permissions in the key policy.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Update the CMK key policy, or add a tightly scoped grant, to allow the partner role the required KMS actions through S3.
When using a customer-managed KMS key (CMK) for SSE-KMS in a cross-account scenario, the key policy must explicitly grant the partner account's IAM role the necessary KMS actions (kms:Decrypt, kms:GenerateDataKey) to allow S3 to perform the encryption/decryption on behalf of the partner. Without this policy update or a tightly scoped grant, the KMS service will deny the request even if S3 bucket policies are correctly configured.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Replace SSE-KMS with S3 object ACLs so the partner account can bypass KMS authorization.
Why it's wrong here
ACLs control S3 object access, not KMS cryptographic authorization. The error is coming from KMS decrypt operations, so ACL changes would not solve it.
- ✗
Create a new bucket in the partner account and copy the objects there to avoid cross-account encryption.
Why it's wrong here
Moving the data would avoid the immediate trust problem, but it is an architectural workaround, not the required fix. It adds duplication, cost, and operational complexity without addressing the KMS sharing requirement.
- ✗
Switch the bucket to SSE-S3 so the partner role no longer needs KMS permissions.
Why it's wrong here
SSE-S3 removes customer-managed key control, which may violate security or compliance requirements. The scenario requires safe use of the customer-managed KMS key, not eliminating it.
- ✓
Update the CMK key policy, or add a tightly scoped grant, to allow the partner role the required KMS actions through S3.
Why this is correct
Cross-account access to SSE-KMS encrypted objects requires KMS authorization in addition to S3 authorization. The key policy must trust the partner role, and the permissions should be limited to the needed KMS actions such as Decrypt, Encrypt, and GenerateDataKey with a service condition for S3. That is why the partner can have valid S3 permissions and still fail until the KMS policy is fixed.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
Go deeper
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SAA-C03 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SAA-C03 exam.